The present invention relates to a reflection-type projection screen useful for receiving an image projected by a projector.
With respect to the projection screen useful for receiving an image projected by a projector, the following proposals have conventionally been made.
In Japanese Utility Model Registration No. 30811, it is proposed that a film containing a resin binder and aluminum powder dispersed therein, formed on the surface of a projection screen is utilized as the light-diffusing and light-reflecting surface of the projection screen.
In Japanese Utility Model Laid-Open Publication No. 40835/1989 and Japanese Patent Laid-Open Publication No. 88263/1993, it is proposed that a resin layer in which a so-called pearl pigment made from mica flakes or mica flakes coated with a titanium dioxide film is dispersed is used as the light-diffusing and light-reflecting surface of a projection screen.
In Japanese Patent Laid-Open Publication No. 53945/1992, it is proposed that a light-diffusing layer made of a transparent resin layer in which calcite powder serving as a light-diffusing agent of low light absorption is dispersed is laminated on a light-reflecting layer.
However, these conventional techniques respectively have the following shortcomings.
The projection screen of Japanese Utility Model Registration No. 30811 is disadvantageous in that when the luminance of reflected light is increased, the reflection of light becomes nearly equal to mirror reflection, and the angle of diffusion thus becomes narrow and that when the angle of diffusion is increased, on the contrary, the luminance of reflected light is decreased. Moreover, this projection screen is also insufficient in the contrast between light and darkness, which is one of the properties required for projection screens.
The projection screen proposed in Japanese Utility Model Laid-Open Publication No. 40835/1989 or in Japanese Patent Laid-Open Publication No. 88263/1993 is superior to the above-described projection screen of Japanese Utility Model Registration No. 30811 in any of the luminance of reflected light (gain), the angle of diffusion (half value angle) and image contrast.
In recent years, however, it has been required to further improve the luminance and image contrast without decreasing the angle of diffusion. The projection screens proposed in the above two publications cannot meet this requirement. This demand is very strong particularly in the field of screens for use in household reflection-type television receivers which are used under such conditions that the luminance of projection light is relatively low and that extraneous light (sunlight, lamplight, etc.) cannot be completely shut off.
The projection screen proposed in Japanese Patent Laid-Open Publication No. 53945/1992 has been improved in luminance (gain), but is still insufficient in contrast as compared with the previously-mentioned projection screen described in Japanese Utility Model Laid-Open Publication No. 40835/1989.
Thus, it has been impossible to obtain any of the desired luminance of reflected light, angle of visibility and contrast by the conventional reflection-type projection screens.